Transverse momentum dependence of charmonium suppression in Pb - Pb collisions at the CERN SPS

Charmonium suppression in Pb-Pb collisions at 158 GeV/c per nucleon is investigated in detail with the study of the transverse momentum distributions of J/ ψ as a function of the centrality of the collision. It is shown that the observed J/ ψ suppression in Pb-Pb interactions is particularly significant mainly at low transverse momentum where it strongly depends on centrality. For peripheral Pb-Pb collisions, the transverse momentum dependence of the J/ ψ cross section is, as a function of centrality, qualitatively similar to the dependence observed in p-A and S-U collisions. Comparing peripheral and central Pb-Pb collisions, the data show a relative suppression in the whole p T range although its amplitude significantly decreases with increasing p T and becomes almost p T independent for the highest p T values.